Characterization of a RecQ Helicase Hrq1 in Saccharomyces cerevisiae

초록

RecQ helicases are involved in the maintenance of genome stability from Escherichia coli to humans. Sgs1 is the only known member of the RecQ helicase family in Saccharomyces cerevisiae, which is the functional homolog of human BLM and WRN helicases. In this study, we found a novel S. cerevisiae homolog of RecQ helicase, Hrq1, by bioinformatic analysis. Hrq1 shows identity of 25% and similarity of 41% with human RecQ4 helicase. Purified recombinant Hrq1 protein revealed both DNA-dependent ATPase and helicase activities in 3’ to 5’ direction. Hrq1 also showed DNA annealing activity, which was proved to be an intrinsic enzyme activity of RecQ4. Unlike weak helicase activity of RecQ4, however, Hrq1 displaced duplex DNA as long as 90 bp. The helicase activity of Hrq1 was stimulated by a fork structure and/or a long single-stranded DNA template region. A mutant yeast strain lacking both Hrq1 and Sgs1 showed markedly reduced viability compared to those of wild-type as well as single mutant strains, suggesting that Hrq1 may play an important role in the maintenance of genome stability in an Sgs1-independent manner.